Governor Stevens T. Mason called out the state militia to keep the Patriots, Canadian rebels, from using Michigan as a base to attack the British government in Canada. Patriot sympathizers had raided the arsenal in Detroit and seized the schooner Anne for an invasion of Canada.
Source : Pasty Central Day in History
For more information, see :
To free upper Canada : Michigan and the Patriot War, 1837-1839 / by Roger L. Rosentreter. Thesis (Ph.D)–Michigan State University. Dept. of History, 1983. 237pp. 123 767 THS Also available online to the MSU Community.
The Patriot War along the Michigan-Canada border : raiders and rebels / Shaun J. McLaughlin. Charleston, SC : The History Press, 2013.